The present invention relates to a method as defined in the preamble of claim 1. Furthermore, the invention relates to a system as defined in the preamble of claim 12.
The regulation systems used in welding workshops are used to adjust the temperature and amount of air blasted into the workshop. The main purpose of ventilation in welding workshops is to remove the impurities produced in welding work from the workshop in a manner as energy-efficient as possible, yet without compromising on the quality of indoor air.
A commonly used method is a ventilation system based on constant air flow, in which the ventilation in a welding workshop is operated with a constant air flow. Ventilation regulation systems also often employ an expedient whereby the air flow is halved on the basis of outdoor temperature. The air flow, i.e. typically the fan speed, is reduced e.g. to half the design value when the outdoor temperature falls below a set limit, a typical limit being xe2x88x9215xc2x0 C.
Another common practice is to provide the system with a timing feature, allowing the user to set the operating times of the ventilation system according to the working hours observed in the workshop. As for regulation, conventional ventilation systems also comprise temperature regulation equipment, and they may comprise regulation equipment for heat recovery.
The above-described conventional solution for the regulation of ventilation systems in welding workshops consumes energy in heating the air and in operating the motors of the supply and extract air fans.
The design of ventilation in a welding workshop is based on a theoretically pre-estimated impurity load produced in the workshop in a maximum load situation. In defining the ventilation, the designer has to use various coefficients to achieve a sufficient level of ventilation. The ventilation is designed by considering the factors affecting the quality of air in the working area, including: geometry of welding hall, welding methods, materials to be welded, number of welders, possible independent arrangements, method of supply air blasting, possible local extraction and its type. Another factor affecting the design is whether recirculation of air is employed or not. /Work Safety Fund (Tyxc3x6suojelurahasto), Report, Workshop-specific ventilation instructions, workshop II, Methods for the solution of ventilation in a welding workshop ZT-05311-08; 1983-08-11, page 26/. Designed on these principles, the air flow is guaranteed to be right in respect of impurities in the worst case, but absolutely too large when the extent of welding activities is lower than in the design situation. In literature, the design rule used for air renewal in welding workshops is a coefficient of 2-6 times per hour.
In conventional systems, air is renewed uniformly regardless of the actual need for ventilation, i.e. the amount of impurities produced in welding work. This leads to a standard fan motor power and excessive energy consumption by the fans and the air heating system during periods when the impurity load is smaller than in the situation for which the air flow was designed.
As stated above, in prior-art ventilation systems for welding workshops, the constant level of general ventilation is always designed for the worst possible situation. For example, the impurity load produced when stainless steel is being welded is heavier than usual, and if stainless steel is welded in a welding workshop, the designer assumes that stainless steel may be welded at all welding stations in the workshop, which further increases the volume of general ventilation. In practice, however, it is not nearly in all situations that the maximum level of general ventilation is needed; instead, in many cases the required volume of general ventilation may be only half the maximum volume. Prior-art solutions have led to an excessive consumption of electric and thermal energy.
Especially in welding workshops where there is considerable variation in the amount of welding work, the above-described system wastes energy as the volume of ventilation is larger than necessary, and thus it increases the environmental stress via emissions in energy production. It can be stated that in many cases ventilation consumes the largest amount of heating energy, and sometimes the fans needed for ventilation are responsible for a significant proportion of the total electricity consumption. Therefore, there is a significant energy saving potential.
For the regulation of ventilation in welding workshops, there are also systems provided with equipment for the measurement of air contamination. Measuring systems based on air contamination can be used to control e.g. the efficiency of ventilation in a welding workshop. However, these systems have not been favored in the regulation of ventilation in welding workshops. This is due to their unreliable operation in demanding conditions, e.g. in welding workshops in metal industry. The reflection density measurements used to measure air contamination have the drawback that they do not detect all the gaseous impurities produced in welding.
When air contamination in a welding workshop is measured using a separate sensor, one of the problems encountered is how to decide which is the right place for the sensor in the welding workshop in respect of air contamination. Sensors measuring air contamination are also very expensive and have a poor performance, which is why they are very seldom used. Because of the large investment costs involved, these systems are economically usable in only very rare cases where the savings achieved via regulation of ventilation are large enough to guarantee a reasonable period of repayment of the investment.
As an example of prior-art technology, reference is made to specification DE 34 34 519 A, which concerns a method and system for extracting welding fumes from the welder""s protective mask by means of a suction hose via a funnel placed on the front side of the protective mask. A suction fan or check valve placed in the suction hose is turned on and off on the basis of the start or end of the flow of welding current or wire feed. The suction intensity can be varied on the basis of the magnitude of the welding current. In this specification, the extraction suction from the welding mask is regulated and the welding current, i.e. the current supplied from the welding machine to the welding gun, is measured. Usually the welding current is direct current, which involves the problem that measuring direct current is difficult and the required measuring equipment is very expensive. Moreover, measurement based on wire feed is naturally not applicable to any other welding method. In the specification, the welding current (d.c.) of one machine is measured. The current may be hundreds of amperes for each welding machine, which is why building a measuring system is expensive and difficult especially in the case of a welding workshop containing several welding machines.
The object of the invention is to disclose a control engineering solution which makes it possible to eliminate the drawbacks of prior-art technology economically as profitably as possible.
The method and the system of the invention are characterized by what is presented in the claims below.
According to the method of the invention, the load imposed on the electrical power network by the electric welding equipment is determined and, based on this determination, the volume of supply air and/or extract air is adjusted so as to achieve a level of ventilation proportional to the impurity load.
Correspondingly, the system of the invention comprises measuring equipment for generating a measurement signal corresponding to the load imposed on the electric power network by the electric welding equipment, and a set of control equipment has been arranged to adjust the volume of supply air and/or extract air on the basis of the measurement signal so as to achieve a level of ventilation proportional to the impurity load.
In the solution of the invention, the load imposed on the electric power network by a welding machine, a welding machine center or multiple-operator welding systems as used in industry is measured. This load is a direct indication of the extent of welding work done in the workshop and of the impurity load it produces in the welding workshop. It has been established via measurements that the load may vary a great deal, which is why regulation of ventilation based on the load is a sensible solution. The regulation solution of the invention significantly reduces the amount of heating energy consumed via ventilation, the amount of energy consumed by the fans as well as the maintenance costs of the ventilation plant.
The invention allows great savings to be achieved in the thermal and electric energy consumed by the ventilation equipment. Regulation of the volume of air flow affects the consumption of both thermal and electric energy. It is possible to save as much as 30% of the thermal energy consumed annually, which means a saving of about 60-65% in the electric energy consumed by the fans, provided that the speed of rotation of the fans is controlled by a frequency converter. In other words, if the air flow is reduced from 100% to 70%, then the electric power requirement of the fans will fall to about 35%.
The regulation solution is advantageous in respect of the cost of construction and operation. The system can also be utilized in corresponding other applications in which the volume of ventilation is defined on the basis of the impurity load and in which the magnitude of the impurity load can be determined with a sufficient accuracy as mentioned above.
In an embodiment of the method, general ventilation in the welding workshop and/or welding station-specific local ventilation are/is regulated. The method and system are also excellently suited for application in welding workshops provided with local ventilation systems based on recirculation of air, in which the welding fumes are filtered but gaseous impurities are not, in which case the gaseous impurities have to be removed by general ventilation. According to the invention, both general ventilation and local ventilation can be regulated, jointly or separately. Sometimes both general and local ventilation systems are in use, and both can now be regulated in accordance with the need for ventilation.
In addition, the method and system of the invention are also applicable for use in welding workshops in which local ventilation is difficult to use and is replaced with general ventilation as far as possible. In many cases, the use of local extraction has also been restricted because in shielded arc welding local extraction undesirably tends to remove the shielding gases as well. Therefore, there is a trend toward replacing local ventilation with forced general ventilation, which is then designed to cover even that part of ventilation that would otherwise have been taken care of using local ventilation. By regulating this kind of forced general ventilation by the method of the invention, significant cost savings will be achieved.
In an embodiment of the method, the volume of supply air and/or extract air is regulated using discontinuous control methods known in themselves. A discontinuous control mode may be implemented be e.g. using two-level (on-off) control or so-called intermediate position control (two-level control with a rest position, three-point control).
In an embodiment of the method, the volume of supply air and/or extract air is regulated using continuous control methods known in themselves. The continuous control may be implemented using e.g. proportional control, proportional plus integral control or proportional plus integral plus derivative control. The volume of supply air and/or extract air may be regulated using e.g. follower control in which the reference variable is determined on the basis of measurement data collected from load information about the welding machines in the welding workshop. Other known control methods may also be applied in the regulation of the volume of supply and/or extract air. To achieve a sufficient smoothness of regulation, the reference variable for the control of the volume of supply and/or extract air (initial data for the regulator) is given with a delay as compared with the value of the reference variable obtained from the load measurement.
In an embodiment of the method, the temperature of supply air is regulated on the basis of the above-mentioned load determination. Reducing the supply air temperature results in more effective extraction of impurities from the welding workshop, socalled thermal deplacement being achieved especially via deplacement ventilation. As the supply air is cooler than the indoor air, it descends toward the floor surface of the welding workshop, thermally deplacing the welding fumes in the working zone.
In an embodiment of the method, the volume of supply and/or extract air is regulated in conventional ways, which may be selected from the following:
damper control by means of a damper or a supply/extract air valve;
control of the rotational speed of the fan motor using two single-speed motors, a so-called Dalander circuit, a multi-speed motor, a gearing, an electric frequency converter and a cage induction motor, a direct-current motor with thyristor control;
control of fan speed using a hydraulic switch
blade angle control, changing the pressure difference and air flow by varying the angular position of the fan blades;
leading blade control, with a leading blade controller mounted at the suction inlet of the fan, creating in the air flow a rotary motion in the direction of rotation of the blade wheel;
eddy current switch.
In an embodiment of the method, the load imposed by the welding equipment on the electric power network is determined by measuring the magnitude of the current, power, energy, reactive power and/or reactive energy consumed by the welding equipment.
In an embodiment of the method, the utilization time of the load imposed by the welding equipment on the electric power network is determined.
In an embodiment of the method, the level of the load imposed on the electric power network by welding devices (welding machine assemblies and/or individual welding machines) using different welding methods is measured; and the volume of supply and extract air is regulated by weighting its adjustment by predetermined weighting values corresponding to different welding methods being used. Since different welding methods produce different impurity loads, it will be advantageous to define for different welding methods different weighting values influencing the regulation of the volume of supply and/or extract air. The selection of weighting for each welding method may be made automatically or manually.
In an embodiment of the system, the control equipment comprises regulating devices for the regulation of the volume of supply and/or extract air and a computation and control unit for receiving a measurement signal from measuring equipment and for giving to the regulating devices a control signal proportional to the measurement signal.
In an embodiment of the system, the ventilation equipment comprises equipment for general ventilation in the welding workshop.
In an embodiment of the system, the ventilation equipment comprises welding station-specific local ventilation equipment.
In an embodiment of the system, the ventilation equipment comprises a supply air fan and a first motor for driving the supply air fan; and the control equipment comprises a first regulator for regulating the rotational speed of the first motor.
In an embodiment of the system, the ventilation equipment comprises an extract air fan, a second motor for driving the extract air fan; and the control equipment comprises a second regulator for regulating the rotational speed of the second motor.
In an embodiment of the system, the first regulator and/or the second regulator is a frequency converter.
In an embodiment of the system, the control equipment comprises mechanical and/or electrical regulating means for the regulation of the volume of supply air and/or extract air.
In an embodiment of the system, the measuring equipment has been arranged to measure the magnitude of the current, power, energy, reactive power and/or reactive energy consumed by the welding equipment.
In an embodiment of the system, the welding equipment comprises an electricity supply center, such as a main distribution center, a rising center, a control center and/or a group distribution center, to which electricity supply center are connected a number of welding machines receiving their welding current from said electricity supply center, and that the measuring equipment has been arranged to measure in the electricity supply center the load imposed on the electric power network by the welding equipment. The load imposed on the electric power network can be measured considerably more easily from an electricity supply center feeding several welding machines. In this way, the load imposed on the electric power network by a plurality of welding machines in the same workshop can be measured by means of a single or a few cheap measuring devices.
In an embodiment of the system, the measuring equipment comprises a current transformer which is connected to the power supply line feeding the welding equipment for generating a measurement signal to be taken to a regulator, said transformer being placed on the side of the electric power network. Measuring the load by means of a current transformer is an advantageous solution because there are commercially available current transformers which can be connected to logic circuits and supervisory relays and which provide a standard current or voltage output applicable to the inputs of these systems.
In an embodiment of the system, the power supply line is a three-phase current line, the current transformer being connected to one of the phases. A reliable measurement result is thus obtained in a very simple manner as the load imposed by the machines is symmetrical on the side of the electric power network, in other words, each phase of the three-phase supply line carries an equal current. Welding machines are usually of a three-phase design.
In an embodiment of the system, the measuring equipment has been arranged to measure the operating time of the welding equipment.
It is possible to integrate with the control equipment even other facilities for the regulation of general ventilation. These may include e.g. regulation of the volume of recirculated air, regulation of supply air temperature, regulation of heat recovery equipment, regulation of pressure in the air ducts, regulation of temperature in the workshops, etc. Using an integrated system, it is possible to optimize the regulation with respect to ventilation because, in addition to the volume of air flow, the system takes into account other aspects of regulation of ventilation as well.